Re: Setting of Points

[signal_spotter@my-deja.com]

In article <ikHz5.58120$c5.160289@newsfeeds.bigpond.com>,
  "Bernard Smith" <epping.smiths@gatewaynet.bigpond.com> wrote:
> I have a question about the setting of points.
>
> Gordon station (NSW) has a terminating road that normally accepts Down
> trains so they can return to the City.  This road can also be used
for Up
> trains to terminate and return to Hornsby during trackwork and
emergencies.
> Looks something like this.
>
>                       ----------------                      Down
> --------------<                          >[a]----------->>>
>                      >------------[b]<
> <<<---------<                         >[c]-----------------
>  Up                ----------------
>
> For safe operation, the points at the Down end of the terminating
road [b]
> can be * paired with the departure points onto the Down [a], * paired
with
> the arrival points from the Up [c] or * 'paired' with both (and put
in a
> split position if no movement is planned at the Down end).
>
> With a train arriving on the Up, and a train in the middle road, I
noticed
> this morning that those points were set in the direction of the Up.
That
> is, a Down terminator could end up heading wrong way on the Up if it
failed
> to stop.
>
> I am sure that there is signal protection and a trip on the middle
road, but
> why would those points be set so as to allow a head-on on the Up?  A
safer
> setting would be to set them to return a shootthrough to the Down.
>
>
Well Bernard, I designed the signalling interlocking at Gordon (and
Lindfield and the auto sections from Nth Syd to Waitara) when I was
with State Rail so hopefully I can answer your query. With facing
points, they are not normally set normal unless there is a conflicting
move set or a track occupied in the overlap or no valid overlap
available through the points reverse or there is a set of trailing
points locked reverse in the facing points reverse overlap. So even
though the overlap was set to the Up main, if the route was set it
would have set those points normal (and locked them). As a last line of
defence the track circuits would have held the aspect to red as well.

regards Ian
Signal Design Engineer.

PS I'm trying to recall the exact reason from memory here but when I
get back to the office next week I'll have a look at my copy of the
control tables and see why I designed it that way.


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